Ectopic Cervical Thymus which Showed Increased Uptake on
¹⁸F−FDG PET Scan after Chemotherapy of Malignant Lymphoma

Yuki Iwama, Masahiko Fujii, Tomoko Yanai^1）, Kousaku Maeda^2）, Kazuro Sugimura
Department of Radiology, Pediatrics^1）, and Cardiovascular and Respiratory Surgery^2）, Kobe University Hospital

Abstract
Ectopic cervical thymus is an uncommon cause of cervical mass in children and is rarely considered in the differential diagnosis.
　　We report a case of cervical ectopic thymus in an 11-year-old boy after chemotherapy of malignant lymphoma. MR images showed a well-defined homogeneous signal intensity mass in the left carotid sheath. ¹⁸F-FDG PET showed markedly increased accumulation in concurrence with the mass. After chemotherapy, lymphatic tissues can undergo reactive hyperplasia including the thymic rebound phenomenon. Image interpretation of ¹⁸F-FDG PET can be complicated. Ectopic cervical thymus is a very important pitfall in ¹⁸FDG-PET scan.

Keywords： Ectopic cervical thymus, 18F-FDG PET, Chemotherapy, Thymic rebound